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Caspase-9 and effector caspases have sequential and distinct effects on mitochondria

Enrique Cepero1, Anne M King, Lane M Coffey

  • 1Department of Microbiology and Immunology, University of Miami School of Medicine, PO Box 016960 (R-138), Miami, FL 33101, USA.

Oncogene
|July 12, 2005
PubMed

Insights

Inhibiting caspases during intrinsic cell death impacts mitochondrial function. Caspase-9 inhibition prevents reactive oxygen species (ROS) production, while effector caspases may terminate ROS by depolarizing mitochondria.

Area of Science:

  • Cell Biology
  • Mitochondrial Function
  • Apoptosis Signaling

Background:

  • Proapoptotic Bcl-2 proteins trigger mitochondrial outer membrane permeabilization, releasing factors that initiate caspase cascades.
  • The precise roles of caspases in modulating mitochondrial physiology during intrinsic cell death remain incompletely understood.

Purpose of the Study:

  • To investigate the effects of inhibiting caspase-9 and effector caspases on mitochondrial membrane potential, cytochrome c release, and reactive oxygen species (ROS) production during intrinsic apoptosis.
  • To elucidate the mechanisms by which caspases influence mitochondrial function in the context of programmed cell death.

Main Methods:

  • Utilized specific inhibitors for caspase-9 and effector caspases in a cellular model of intrinsic apoptosis.
  • Monitored mitochondrial membrane potential, cytochrome c release, and ROS generation.
  • Assessed the involvement of the electron transport chain complexes (I-IV) in caspase-mediated mitochondrial events.

Main Results:

  • Caspase inhibition prevented complete loss of mitochondrial membrane potential but did not impede cytochrome c release.
  • Inhibition of effector caspases led to mitochondrial uncoupling and increased ROS production, independent of electron transport chain complexes I-IV.
  • Caspase-9 inhibition precluded mitochondrial uncoupling and ROS generation, allowing sustained electron transport despite cytochrome c release.

Conclusions:

  • Activated caspase-9 appears to restrict cytochrome c access to complex III, promoting ROS production.
  • Effector caspases may induce mitochondrial depolarization to limit ROS and maintain the apoptotic state.
  • These findings reveal distinct roles for caspase-9 and effector caspases in regulating mitochondrial function during apoptosis.

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